1. Field of the Invention
This invention relates to an improved magnetic apparatus for precisely positioning an X-Y movable stage with respect to a fixed base and, more particularly, to such a stage suitable for use in a wafer-stepper employed in the photolithographic manufacture of monolithic integrated circuits.
2. Description of the Prior Art
In the past, stepper motors have been used for the purpose of positioning the X-Y stage of a wafer-stepper with six degrees of freedom. Recently, however, prior-art magnetic positioning apparatus has been developed for this purpose. This magnetic positioning apparatus provides substantially higher positioning resolution and other advantages over stepper motors. These other advantages include:
(1) the monolithic nature of such magnetic positioning apparatus allows direct coupling between the metrology system, the stage, and the wafer or substrate,
(2) the direct electromagnetic coupling in all 6 axes eliminates the 25 needed for precision robbing, slow mechanisms such as focus actuators and coarse theta (yaw) adjustment mechanisms;
(3) the design of such magnetic positioning apparatus lends itself to a high bandwidth, servo controlled, positioning system that settles much faster (because of the higher bandwidth) than other types of positioning stage; and
(4) such magnetic positioning apparatus is equally applicable to step-and-repeat or step-and-scan types of operation and does not exhibit cogging that inhibits travel at constant velocity with Sawyer motor based stages.
A first example of a prior-art magnetic positioning apparatus suitable for use in a wafer-stepper is disclosed in U.S. Pat. No. 5,196,745, issued Mar. 23, 1993. The magnetic positioning apparatus disclosed in U.S. Pat. No. 5,196,745 employs a plurality of stage-attached permanent magnetic arrays, each of which comprises a series of adjacent oppositely-poled permanent magnets (i.e., magnetic fields of each pair of adjacent magnets are rotated 180xc2x0 with respect to one another) that cooperate with stationary electromagnetic coil arrays in the horizontal (X, Y) plane, to produce the proper lateral forces to provide desired motion of the X-Y stage in X and/or Y directions. Additional electromagnets provide controllable forces for levitating the stage-attached permanent magnetic arrays"" forces in the vertical (Z) direction with respect to the stationary electromagnetic coil arrays to maintain a desired air gap therebetween and controllable couples for providing small angular rotations of the stage-attached permanent magnetic arrays about the X, Y and/or Z axes.
Known in the art is a so-called Halbach magnetic array, which comprises a series of permanent magnets in which the respective magnets are poled so that the magnetic fields of each pair of adjacent magnets are rotated 90xc2x0 with respect to one another.
A second example of prior-art magnetic positioning apparatus for use in a wafer-stepper is shown in FIGS. 1 and 2 and is described in detail below. However, briefly, this second example comprises four spatially-separated Halbach magnetic arrays extending from each of the four corners of an X-Y stage, with each of the Halbach magnetic arrays cooperating with a stationary electromagnetic coil array in the horizontal (X, Y) plane, thereby achieving (1) controllable lateral forces in the X and Y horizontal directions and (2) controllable levitating forces in the vertical Z direction which are also capable of creating controllable couples for providing small angular rotations about the X, Y and/or Z axes. Thus, this second example of prior-art magnetic positioning apparatus differs from the above-described first example of prior-art magnetic positioning apparatus in that it does away with the need for the aforesaid additional electromagnets for providing both controllable levitating forces in the vertical Z and controllable couples for providing small angular rotations about the X, Y and/or Z axes.
Currently, wafers as large as 300 millimeters (mm) in diameter need to be processed. Thus, the overall horizontal area of the second example of the prior-art magnetic positioning apparatus for use in a wafer-stepper for processing 300 mm is very large (significantly greater than 4xc3x974=16 square feet). The problem caused by this very large horizontal area is that it makes it very hard to adequately support the photolithographic projection optics, while also complicating the layout of the wafer-stepper.
The present invention provides a new configuration of Halbach magnet arrays and electromagnetic coils that leads to a much more compact and energy efficient X-Y stage, thereby solving the aforesaid problem.
More specifically, the present invention provides an improvement in apparatus for magnetically positioning a movable X-Y stage with respect to X and Y horizontal axes and a Z vertical axis. The improved apparatus comprises: (1) a first commutated coil of wire that lies substantially in a first horizontal X-Y plane and is angularly offset in the first horizontal X-Y plane by minus a first oblique angle with respect to said Y axis; (2) a second commutated coil of wire that lies substantially in a second horizontal X-Y plane substantially in vertical alignment with the first horizontal X-Y plane and angularly offset in said second horizontal X-Y plane by plus a second oblique angle with respect to the X axis; (3) a first set of a plurality of flat stationary electromagnetic coils of wire that lie substantially in the first horizontal X-Y plane mid-way between the windings of the first commutated coil of wire and are angularly offset in the first horizontal X-Y plane by minus the first oblique angle with respect to the Y axis; (4) a second set of a plurality of flat stationary electromagnetic coils of wire that lie substantially in the second horizontal X-Y plane mid-way between the windings of the second commutated coil of wire and are angularly offset in the second horizontal X-Y plane by minus the second oblique angle with respect to the X axis; (5) a two dimensional array of magnets including Halbach magnet arrays attached to the movable X-Y stage, wherein the array substantially lies in a third horizontal X-Y plane, is oriented substantially parallel to the same one of the X and Y horizontal axes with respect to which the first and second oblique angles are measured, and is simultaneously situated in a cooperative relationship with both of the first and second commutated coils of wire, and the first and second set of electromagnetic coils of wire; and (6) means for levitating the two dimensional array of magnets in the third X-Y plane.
A first embodiment of the magnet array defining an X-Y-Z coordinate system with each axis perpendicular to each other axis, each magnet having a particular magnetic field orientation and being substantially the same size and shape as every other magnet, the overall magnet array comprising: (1) a first Halbach magnet array, in the form of a first column in an X-Y plane aligned parallel to the Y-axis, the first Halbach magnet array having: (a) a first magnet oriented with the magnetic field extending vertically upward therefrom parallel to the Z-axis; (b) a second magnet adjacent the first magnet with the magnetic field extending horizontally away from the first magnet parallel to the Y-axis; (c) a third magnet adjacent the second magnet with the magnetic field extending vertically downward therefrom parallel to the Z-axis; and (d) a fourth magnet adjacent the third magnet with the magnetic field extending horizontally away from the third magnet parallel to the Y-axis; and (2) a second Halbach magnet array, in the form of a second column in the same X-Y plane as the first column, aligned parallel to the Y-axis and spaced apart from the first column a width of a single magnet in the direction of the X-axis, the second Halbach magnet array having: (a) a fifth magnet aligned opposite the first magnet in the first column with the magnetic field extending vertically downward therefrom parallel to the Z-axis; (b) a sixth magnet adjacent the fifth magnet and opposite the second magnet in the first column with the magnetic field extending horizontally toward the fifth magnet parallel to the Y-axis; (c) a seventh magnet adjacent the sixth magnet and opposite the second in the first column with the magnetic field extending vertically upward therefrom parallel to the Z-axis; and (d) an eighth magnet adjacent the seventh magnet and opposite the fourth magnet in the first column with the magnetic field extending horizontally away from the seventh magnet parallel to the Y-axis; wherein each magnet has an upper and a lower lateral extent in reference to the Y-axis with the upper and lower lateral extent of each magnet in the second column being aligned with the upper and lower lateral extent of the magnet in the first column that the second column is opposite.
A second embodiment of the magnet array defining an X-Y-Z coordinate system with each axis perpendicular to each other axis, each magnet having a particular magnetic field orientation and being substantially the same size and shape as every other magnet, said overall magnet array comprising: (1) a first Halbach magnet array, in the form of a first column in an X-Y plane aligned parallel to the Y-axis, the first Halbach magnet array having: (a) a first magnet oriented with the magnetic field extending vertically upward therefrom parallel to the Z-axis; (b) a second magnet adjacent the first magnet with the magnetic field extending horizontally toward the first magnet parallel to the Y-axis; (c) a third magnet adjacent the second magnet with the magnetic field extending vertically downward therefrom parallel to the Z-axis; and (d) a fourth magnet adjacent the third magnet with the magnetic field extending horizontally away from the third magnet parallel to the Y-axis; (2) a second Halbach magnet array, in the form of a second column in the same X-Y plane as the first column, aligned parallel to the Y-axis and spaced apart from the first column a width of a single magnet in the direction of the X-axis, the second Halbach magnet array having: (a) a fifth magnet aligned opposite the first magnet in the first column with the magnetic field extending vertically downward therefrom parallel to the Z-axis; (b) a sixth magnet adjacent the fifth magnet and opposite the second magnet in the first column with the magnetic field extending horizontally away from the fifth magnet parallel to the Y-axis; (c) a seventh magnet adjacent the sixth magnet and opposite the second in the first column with the magnetic field extending vertically upward therefrom parallel to the Z-axis; and (d) an eighth magnet adjacent the seventh magnet and opposite the fourth magnet in the first column with the magnetic field extending horizontally toward from the seventh magnet parallel to the Y-axis; (3) a third column of magnets in the same X-Y plane as the first and second columns, aligned parallel to the Y-axis and located between, and adjacent to, each of the first and second columns, the third column of magnets having: (a) a ninth magnet between, and adjacent, to both of the first and fifth magnets with the magnetic field extending horizontally toward the first magnet parallel to the X-axis; and (b) a tenth magnet between, and adjacent to, each of the third and seventh magnets with the magnetic field extending horizontally away from the third magnet parallel to the X-axis; and (4) a fourth column of magnets in the same X-Y plane as the first, second and third columns, aligned parallel to the Y-axis and located adjacent to the second column on the side of the second column away from the first column, the fourth column of magnets having: (a) an eleventh magnet adjacent to the fifth magnet with the magnetic field extending horizontally away from the fifth magnet parallel to the X-axis; and (b) a twelfth magnet adjacent to the seventh magnet with the magnetic field extending horizontally toward the seventh magnet parallel to the X-axis; wherein each of the magnets has an upper and a lower lateral extent in reference to the Y-axis with the upper and lower lateral extent of each magnet in the second column being aligned with the upper and lower lateral extent of the magnet in the first column that the second column is opposite, and the upper and lower lateral extent of the ninth, tenth, eleventh and twelfth magnets in the third and fourth columns, respectively, being aligned with the upper and lower lateral extent of each magnet in the first or second column that the magnet is the to be adjacent.